Persona: Santa Marta Pastrana, Cristina María
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Santa Marta Pastrana
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Cristina María
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Publicación Multiresolution Reconstruction for Cone-Beam Tomography from Raw Data Projections Using 3D Ridgelets(Springer Nature, 2011-03-01) Romero, Eduardo C.; Gómez Gómez, Francisco; Santa Marta Pastrana, Cristina MaríaThis paper presents a novel method which reconstructs any desired 3D image resolution from raw cone-beam CT data. X-ray attenuation through the object is approximated using ridgelet basis functions which allow us to have multiresolution representation levels. Since the Radon data have preferential orientations by nature, a spherical wavelet transform is used to compute the ridgelet coefficients from the Radon shell data. The whole method uses the classical Grangeat’s relation for computing derivatives of the Radon data which are then integrated and projected to a spherical wavelet representation and back-reconstructed using a modified version of the well known back-projection algorithm. Unlike previous reconstruction methods, this proposal uses a multiscale representation of the Radon data and therefore allows fast display of low-resolution data level.Publicación A sparse Bayesian representation for super-resolution of cardiac MR images(Elsevier, 2017-02) Velasco, Nelson F.; Rueda Olarte, Andrea del Pilar; Romero, Eduardo C.; Santa Marta Pastrana, Cristina MaríaHigh-quality cardiac magnetic resonance (CMR) images can be hardly obtained when intrinsic noise sources are present, namely heart and breathing movements. Yet heart images may be acquired in real time, the image quality is really limited and most sequences use ECG gating to capture images at each stage of the cardiac cycle during several heart beats. This paper presents a novel super-resolution algorithm that improves the cardiac image quality using a sparse Bayesian approach. The high-resolution version of the cardiac image is constructed by combining the information of the low-resolution series –observations from different non-orthogonal series composed of anisotropic voxels – with a prior distribution of the high-resolution local coefficients that enforces sparsity. In addition, a global prior, extracted from the observed data, regularizes the solution. Quantitative and qualitative validations were performed in synthetic and real images w.r.t to a baseline, showing an average increment between 2.8 and 3.2 dB in the Peak Signal-to-Noise Ratio (PSNR), between 1.8% and 2.6% in the Structural Similarity Index (SSIM) and 2.% to 4% in quality assessment (IL-NIQE). The obtained results demonstrated that the proposed method is able to accurately reconstruct a cardiac image, recovering the original shape with less artifacts and low noise.Publicación Motion estimation of tagged cardiac magnetic resonance images using variational techniques(Elsevier, 2010-09) Carranza Herrezuelo, N.; Bajo, A.; Sroubek, F.; Cristobal, G.; Santos, A.; Ledesma Carbayo, M. J.; Santa Marta Pastrana, Cristina MaríaThis work presents a new method for motion estimation of tagged cardiac magnetic resonance sequences based on variational techniques. The variational method has been improved by adding a new term in the optical flow equation that incorporates tracking points with high stability of phase. Results were obtained through simulated and real data, and were validated by manual tracking and with respect to a reference state-of-the-art method: harmonic phase imaging (HARP). The error, measured in pixels per frame, obtained with the proposed variational method is one order of magnitude smaller than the one achieved by the reference method, and it requires a lower computational cost.Publicación Intraventricular vortex properties in nonischemic dilated cardiomyopathy(American Physiological Society, 2014-03-01) Bermejo, Javier; Benito, Yolanda; Alhama, Marta; Yotti, Raquel; Pérez del Villar, Candelas; Pérez David, Esther; González Mansilla, Ana; Barrio, Alicia; Fernández Avilés, Francisco; Álamo, Juan C. del; Martínez-Legazpi Aguilo, Pablo; Santa Marta Pastrana, Cristina MaríaVortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1–74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m2/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound. intraventricular vortex dynamics may have an important role in cardiac hemodynamics. During early filling and atrial contraction, strong jets entering the left ventricle (LV) lead to the formation of vortex rings near the tips of the mitral valve leaflets. Due to the chiral configuration formed by the LV inflow tract, main chamber, and LV outflow tract (LVOT), these vortex rings evolve into large rotational flow structures that occupy a large fraction of the ventricle. Recent clinical data in patients with diastolic dysfunction indicate that LV vortices may facilitate flow from the left atrium to the LV apex (6). Also, vortical structures may increase ejection efficiency by conserving the momentum of blood built up during filling (1). Finally, vortices may contribute to blood mixing inside the ventricle, avoiding stasis (6, 19, 30, 32, 33, 40). Because impaired diastolic function, reduced mechanical efficiency, and risk of thrombosis characteristically concur in patients with nonischemic dilated cardiomyopathy (NIDCM), addressing the physical properties of intraventricular vortices is particularly relevant in this condition. Recent ultrasound (1, 19, 29), computational (28), and phase-contrast magnetic resonance (PC-MR) (3, 6, 11–13) studies have described intraventricular flow characteristics in small numbers of patients with normal and dilated hearts. We hypothesized that significant physiological insights can be gained by comprehensively studying the temporal dynamics and correlates of intraventricular vortex development. We also hypothesized that impaired chamber properties in patients with NIDCM may be associated with modified vortex physiology. Therefore, the present study was designed to characterize the dynamics of vortex position, size, and strength along the cardiac cycle in patients with NIDCM and age-matched healthy control subjects. The physiological relevance of vortices relative to the global LV kinetic energy (KE) balance was also analyzed in detail. We used a custom-developed method that allowed us to measure two-dimensional (2-D) flow using conventional color-Doppler ultrasound (17). Because most previous evidence in this field has been reported using PC-MR, the ultrasound-based method was compared in vivo against this technique in a subset of NIDCM patients.